Transparent, laminated, light polarizing glasses are used extensively in the making of medical, ophthalmic, sun, and protective spectacle lenses, but they could also be utilized in other fields as, for example, instrument lenses, windows for vehicles of all kinds (air, sea, land), windows for buildings, and the like.
The manufacture of polarizing glasses raises various problems related to the solubility of the polarizing materials (generally the polarizing particles) in the surrounding environments (water, chemical products even in weak concentrations, etc.), as well as their very low mechanical strength. This has led researchers to devise various means of protection as, for example, by incorporating the polarizing particles in a polymer film.
In general, the products are recognized as having very low surface hardness, a very marked sensitivity to scratching, and an incompatibility with the majority of the current cosmetic products.
For all that, attempts to obtain glass lenses have consisted in associating an organic polarizing film of the polyvinyl alcohol type with one or two ("sandwich") elements of glass. These attempts have come up against a number of difficulties such as:
the complexity of bonding the polarizing film to an optical substrate without deforming the direction of polarization, as indicated in French Patent No. 76.18891, filed Jun. 22, 1976 by American Optical Corporation;
the weight of the assemblies thus obtained are not compatible with, for example, the conventional lenses utilized in spectacles (10-25 grams); and
the extremely high cost of such products which is a result of their complexity.
For these reasons, these products are not much used for applications of the "general public" type such as spectacle making.
More recently, attempts were conducted to provide polarizing films of the polyvinyl acetate or polyvinyl butyrate type bonded onto the concave face of an inorganic spectacle glass. This approach also proved fruitless because of three major difficulties:
the very poor optical quality of such films; PA1 the necessity for protecting them from moisture; and PA1 their sensitivity to scratching.
In spite of all these handicaps, a product of this type is available in commerce under the name of "POLAROID" lenses. In this product the polarizing material is contained in polyvinyl films laminated front and back to thin films of cellulose and protected by a thin strip of melamine.
As with all materials of this type, the great disadvantage in using this type of product is its very great sensitivity to scratching when compared to conventional products which are inorganic glasses.
In addition to all this, all the products currently (or formerly) on the market do not satisfy a present need of consumers which is to have at their disposal inorganic photochromic glasses (that is to say an optical transmission which varies with the conditions of lighting) and polarizing, colorable, and/or filtering if it is needed. Such a product in order to be perfectly suitable, should not be subject to any limitation about the design of the shape and the radius of curvature in order to satisfy, without any restriction, all the needs for making medical, ophthalmic, and protective spectacles.